Je zei:
How is the time registration arrange on a satelite?
Is it arranged with an electronic, electrical circuit?
Is it arranhed with an atomic clock or a laser?
Satellites use multiple, layered mechanisms for timekeeping. Here is the clear structure:
Most navigation and scientific satellites (GPS, Galileo, GLONASS, BeiDou, ESA deep-space missions) carry atomic clocks.
Typical atomic clocks used:
Cesium atomic clocks
Rubidium atomic clocks (most common in GPS)
Hydrogen maser clocks (Galileo, ESA deep-space)
Laser-pumped atomic clocks (modern, more stable)
These clocks define the satellite’s internal “master time” with accuracies around 10⁻¹² to 10⁻¹⁵.
So the time generation is done by atomic transitions, not electronics alone.
Although time originates from the atomic clock, electronics are used for:
Electronic circuits divide or multiply the atomic frequency into:
10.23 MHz (GPS)
10 MHz, 100 MHz, etc.
Through low-jitter electrical lines and clock distribution boards.
Electronic PLLs keep derived clocks synchronised to the atomic standard.
Satellites usually carry multiple atomic clocks that can be hot-swapped by electronics if one begins drifting.
So, electronics route and maintain the timing, but do not generate the absolute time.
Yes, but only in advanced atomic clocks:
Used in:
ESA Galileo IOV + FOC satellites (Passive Hydrogen Maser uses microwave, but next-gen uses lasers)
NASA deep-space atomic clock (DSAC)
Laboratory clocks becoming space-ready (optical clocks)
Lasers are used to:
cool atoms
manipulate atomic states
interrogate optical transitions
But they are part of the atomic clock, not a separate timing method.
| Component | Function |
|---|---|
| Atomic clock | Primary time reference (Rubidium, Cesium, Hydrogen Maser, optical/laser-pumped). |
| Electronics | Distribute, stabilize, and use the atomic clock signal. |
| Lasers | Used inside modern atomic clocks (optical clocks, laser pumping, cooling). |
| No normal electrical oscillator alone | Not accurate enough → would drift meters per second for GPS. |
A satellite keeps time with an atomic clock.
Electronics distribute and stabilize the signal.
Lasers are used inside advanced atomic clocks.
If you want, I can also explain:
why relativistic corrections must be applied (+38 µs/day)
how GPS satellites synchronise time with Earth
how the clock signal is encoded in the radio navigation message.
Yes — those numbers refer to fractional time accuracy, meaning seconds per second.
Here is what they mean:
This is a dimensionless fraction, but its effect is on seconds.
A clock with 10⁻¹² stability drifts about
1 picosecond (10⁻¹² s) per second
A clock with 10⁻¹⁵ stability drifts about
1 femtosecond (10⁻¹⁵ s) per second
| Stability | Drift per day |
|---|---|
| 10⁻¹² | ~100 nanoseconds/day |
| 10⁻¹³ | ~10 nanoseconds/day |
| 10⁻¹⁴ | ~1 nanosecond/day |
| 10⁻¹⁵ | ~0.1 nanosecond/day |
GPS needs accuracy around 1–10 nanoseconds, so this matches well.
1 nanosecond of timing error → 30 cm of position error.
So atomic clocks with 10⁻¹³ or better stability keep GPS distances accurate.
Yes, the 10⁻¹² to 10⁻¹⁵ refers to the time error in seconds, expressed as a fractional stability per second.
If you want, I can also:
convert this to frequency accuracy (Hz)
show how this determines GPS position accuracy
show how the relativistic correction of +38 µs/day compares to these tiny errors.
Yes — we can write the exact physical law for how a satellite’s clock runs slower or faster depending on distance from Earth’s center, including all physical influences.
Below is the clean GR-correct formula.
For a non-rotating, spherically symmetric Earth (Schwarzschild metric), the rate of a clock at radius r compared to a clock far away is:
dtdτ=1−rc22GM Where:
dτ = proper time on the satellite
dt = coordinate time far from gravity
G = gravitational constant
M = Earth’s mass
r = distance from Earth’s center
c = speed of light
For small potentials (true for Earth), this can be approximated:
dtdτ≈1−rc2GMThis shows the fundamental dependence: higher altitude → less gravitational potential → time runs faster.
A moving clock suffers special relativistic time dilation:
dtdτ=1−c2v2 A satellite moves fast → its time runs slower.
The complete expression to first order (valid for Earth satellites):
dtdτ≈1−rc2GM−2c2v2This is the actual formula used for GPS relativistic corrections.
Term 1: −rc2GM → GR gravitational time dilation
Term 2: −2c2v2 → SR velocity time dilation
These two effects compete:
Gravity makes the satellite’s clock run faster.
Speed makes it run slower.
For GPS, the net effect is +38 microseconds/day faster than Earth clocks.
Gravitational time dilation
−rc2GM
Velocity time dilation
−2c2v2
Earth’s rotation (centrifugal potential)
Affects ground clocks, not satellites.
Earth’s quadrupole moment (J₂ term)
Corrections from Earth not being perfectly spherical.
(Very small but used in precision models.)
Orbit eccentricity corrections
Clock rate oscillates slightly over its orbit.
Applied continuously in GPS.
Relativistic frequency shift of the onboard oscillator
Already pre-corrected before launch.
The GPS relativistic correction term for a satellite in elliptical orbit is:
Δtr=−c22r⋅vThis accounts for:
gravitational potential
orbital velocity
orbital eccentricity
It is the operational formula.
I can also compute:
the exact time dilation for any satellite altitude you choose
the difference in seconds/day directly
a graph of time dilation vs. radius (if you want a plot)
Just tell me the altitude or “make the graph”.
Nice question — let’s put numbers on it.
Using
G=6.67430×10−11m3kg−1s−2,
M⊕=5.97219×1024kg,
c=299792458 m/s:
GMc2≈225.4769 m−1
(about 225.48 per metre)
Equivalently it’s useful to give the small length scale GM/c2:
c2GM≈0.00443504 m ≈ 4.435 mm.
(This is the Earth’s gravitational radius — extremely small.)
Earth mean radius: R⊕≈6371 km.
Geostationary altitude above Earth surface: ≈35786 km → radius rGEO≈42157 km (≈ 4.2157×107 m).
GPS / MEO altitude: ≈ 20200 km → radius ≈ 26571 km.
LEO typical altitudes: roughly 200–2000 km → radii ~6.6×106–8.4×106 m. (ISS ≈ 400 km altitude.)
GM/(R⊕c2) (at Earth's surface) ≈ 6.96×10−10.
GM/(rGEOc2) ≈ 1.05×10−10.
GM/(rGPSc2) ≈ 1.67×10−10.
For LEO (~400 km) GM/(rc2) ≈ 6.55×10−10.
These are tiny numbers; they are the terms that enter the approximate gravitational time-dilation formula
dτ/dt≈1−GM/(rc2) (first-order).
Difference of the gravitational term between surface and GEO:
Δ(GM/(rc2))≈5.91×10−10 (surface minus GEO)
That corresponds to ≈ 5.11×10⁻⁵ s/day ≈ 51.1 microseconds per day (gravitational effect alone — GEO clocks run faster).
If you include the special-relativistic slowdown from GEO orbital speed (~3.07 km/s), that removes ≈ 4.5 μs/day, leaving a net of ≈ +46.6 μs/day (GEO clock faster than ground clock).
(For comparison: GPS satellites end up about +38 μs/day net after both effects and other small corrections.)
Because GMc2 ≈ 225.48 m⁻¹, you can quickly convert between the dimensionless potential and a length:
rc2GM=rGM/c2with GM/c2≈0.004435 m.So for any radius r (in metres) just compute 0.004435/r to get GM/(rc2).
If you want, I can:
compute the exact seconds/day difference for any specific satellite altitude you give, or
make a graph of time-dilation (seconds/day) vs altitude from surface up to GEO.
Yes — satellite times are correct per day, but only because they are actively corrected.
If we did nothing, satellite clocks would drift badly compared to clocks on Earth.
Let me explain clearly.
A satellite clock naturally experiences:
Higher altitude → weaker gravity → clock gains time.
High orbital speed → clock loses time.
GPS satellites: would run +38 microseconds/day faster
GEO satellites: would run ≈ +46 microseconds/day faster
LEO satellites: usually run slower, because speed dominates
If left uncorrected, this would cause:
GPS position errors of about 10 km per day
Navigation would become useless in minutes
So the “raw” satellite time is not naturally correct.
GPS atomic clocks are deliberately detuned on Earth before launch.
GPS onboard clock frequency:
fspace=fground(1−4.4647×10−10)This offset exactly cancels the +38 µs/day relativistic gain once the satellite is in orbit.
This means:
On Earth: the clock is wrong
In orbit: it becomes correct
Every navigation satellite (GPS, Galileo, GLONASS, BeiDou):
Has its clock monitored from ground stations
Receives correction updates several times per day
Broadcasts its “clock correction parameters” in the navigation signal
So the system always knows:
the clock bias
the clock drift
the clock drift rate
And corrects for all of them in real time.
but the system mathematically removes its errors.
This is how GPS gives meter-level precision.
Satellite clocks, by themselves, run incorrectly per day.
But the navigation system corrects them continuously so that the effective time is accurate to nanoseconds.
If you want, I can compute:
how many meters of error a 1-nanosecond clock error creates
the exact drift per day for any satellite you choose
a graph showing how the raw clock behaves vs the corrected clock.
You are 100% correct, and let me restate it clearly so there is zero ambiguity:
This is the core statement of gravitational time dilation.
So:
A clock near Earth’s surface runs slower.
A clock high above Earth (like on a satellite) runs faster.
This comes directly from General Relativity.
I wrote:
“Gravity makes the satellite’s clock run faster.”
What this should be read as is:
“The weaker gravitational field at the satellite’s distance makes the satellite’s clock run faster than a clock on Earth’s surface.”
But the shorter wording can be misread.
So your interpretation is correct.
Let me rewrite the principle in the clearest possible form:
Since gravitational potential increases with distance from the mass,
a clock higher up runs faster.
Mathematically:
dtdτ≈1−rc2GMIf r (distance from Earth’s center) increases → the term GM/(rc2) becomes smaller, so the clock rate dτ/dt becomes closer to 1, meaning:
👉 The clock runs faster.
Earth surface clock runs slower
GPS satellite clock runs 45.9 microseconds/day faster (gravitational only)
Then subtract the SR effect (satellite speed slows the clock by 7.0 μs/day):
Final net:
+38.9 μs/day faster than Earth clocks.
If you want, I can express this using your ontology framework too:
and the “local time derivative” belongs to a different relation equation.
Just tell me if you want it written in your ontology format.